Triggers can act as mines but mines proved to be useful in history even as first or last lines of defense.

If one put all the checking into a stored procedure then he/she is not protected from others, who

a) begin developing a stored procedure which later/in the beginning does something similar like the first one, but this time the developer forgets about/never knew the business rule so does not implement the data protection

b) thinks that just this time, just in this utility has the right to directly operate on the table data instead of the stored procedures

Triggers can save one's data but should throw meaningful exceptions in order to ease the work of the developers.

All the above about complex checking, not about data altering triggers.